The present invention relates to optical devices, specifically, panel display, with interactive capabilities, which utilizes optical waveguides, mechanical light-switches, and linear-array light sources.
Conventional television (TV) sets and computer monitors use cathode ray tubes (CRTs) as display devices. The CRTs are undesirably large, heavy, and utilize power inefficiently. Therefore, there is a genuine need to replace CRTs with thin, light weight and energy efficient flat-panel displays (FPDs).
Commercial FPD technologies include liquid crystal displays (LCDs), thin-film electroluminescence (TFEL) displays, plasma display panels (PDPs), field emission displays (FEDs), and light-emitting-diode (LED) matrix displays.
Transmissive matrix-LCDs dominate the current FPD market. This type of displays uses a backlight for illumination. These LCD devices are very inefficient. Before reaching a viewer, a light beam must pass through polarizer layers, liquid crystal layers, color filters, and some electronic component films. In the process, about 95% of the light energy is lost. Moreover, the fabrication processes, especially for active matrix LCDs (AMLCDs), are very complex and expensive. A high resolution AMLCD requires thousands of addressing lines and millions of transistors on a large substrate, therefore manufacturing is expensive. The production of AMLCDs relies on the use of sophisticated semiconductor processes. Particularly, expensive photolithography has to be used. As a result, the diagonal of an affordable display is limited.
Other FPD also suffer limitations. TFEL displays lack efficient blue phosphors and thus have low overall energy efficiency. PDP technology has been used for commercial production, however manufacturing cost is high and high energy-efficiency displays have yet to be demonstrated. FED technology potentially is more energy efficient than liquid crystal based displays, however, this potential has not yet been demonstrated. In addition, manufacturing cost of FEDs currently exceeds that of AMLCDs.
LED matrix displays are composed of pluralities of individual LEDs arranged in a matrix. Recent commercial availability of high-efficiency InGaN-based blue and green LEDs coupled with the existence of high performance AlGaAs- and AlInGaP-based red LEDs has made it possible to form high-brightness, full color LED panel displays. This type of display is presently limited to very large displays such as those used for stadium and outdoor advertisement applications. The main limitations of matrix LED technology include high cost and impractical manufacture of regular sized displays. The high cost is due to the necessity of using a large number of LEDs to make the displays. For example, a 1024xc3x97768 full-color display requires the use of 1024xc3x97768xc3x973=2,359,296 LEDs. Such a display is made by assembling individual LEDs that are usually larger than a couple of millimeters in diameter. It is difficult and costly to make and assemble smaller LEDs. A new approach must be sought if the high performance LEDs are to be used in low-cost flat-panel displays. The present invention provides such an approach.
A less known but viable display technology uses optical waveguides to convey light from a small light source onto a large display screen. Optical fiber projectors (Awai et al., U.S. Pat. No. 4,763,984, (1988)) and stacked planar waveguide projectors (Veligdan, U.S. Pat. No. 5,381,502 (1995) and U.S. Pat. No. 5,455,882 (1995)) are magnifying projectors that channel light images from a small but intense light-image source to a large screen. The construction of an optical fiber projector is fairly complex, due to a huge number of fibers to be assembled. A stacked planar waveguide projector requires an expensive laser scanner or digital micromirror array combined with a sophisticated focusing system as the video source and is, therefore, high cost. In addition, while these two displays can be made relatively compact, neither of them is a true flat-panel display.
Waveguide-based flat-panel displays use planar and channel waveguides (Andrews in U.S. Pat. No. 3,871,747 (1975)). Most of the display devices of this category involve parallel channel waveguides assembled on a flat substrate to form a display screen. Light switches are placed on top or inside the channel waveguides and are distributed across the display screen. Light beams are first injected into the channel waveguides from the side and are then extracted by the light switches at appropriate locations on the display screen to form an image. The main differences among various approaches are the underlying light-extraction mechanisms and the constructions of the light switches. Rockwell (U.S. Pat. No. 5,106,181 (1992) and U.S. Pat. No. 5,009,483 (1991)) described methods of using electro-optical effect, thermal-optical effect, and acoustic effect to alter the optical confinement property of waveguides so as to extract light. Staelin et al. (U.S. Pat. No. 4,822,145 (1989)), disclosed a waveguide display using liquid crystals as the cladding materials of waveguides. By applying an electrical field, one may increase the refractive index of the liquid-crystal cladding layer and, therefore, permit light to escape in a controlled fashion from the waveguides. Nishimura, (U.S. Pat. No. 4,640,592 (1987)), describes a liquid-channel waveguide display. Heat is applied to local regions of the waveguide channels and bubbles are produced in the liquid. These bubbles cause light scattering out of the waveguides. While all these methods can, in principle, extract light out of waveguides, they suffer from low extraction coefficient, high-energy consumption, sluggishness, and/or high manufacturing cost.
Recently, a micromechanical flat-panel display was proposed by Stern (xe2x80x9cLarge-area micromechanical flat-panel display,xe2x80x9d Conf. Record 1997 Int. Display Res. Conf. (Soc. For Inf. Display, Toronto, Canada, Sept. 15-19, 1997), pp. 230-233). The display screen consists of a planar waveguide, on which a matrix of electrostatically driven micromechanical light switches are placed. Fluorescent light tubes are used as the light source of the display. The light extraction from the planar waveguide is achieved by light tunneling from the waveguide into the light switches due to a close proximity the light switches to the waveguide surface (Kim et al. xe2x80x9cMicromechanically based integrated optic modulators and switches,xe2x80x9d Proc. Integrated Optics and Microstructures, SPIE 1793, 183 (1992) and Piska et al. xe2x80x9cElectrostatically actuated optical nanomechanical devices,xe2x80x9d Proc. Integrated Optics and Microstructures, SPIE 1793, 259-272 (1992)). There are several inherent limitations in the proposed embodiment that will prevent the production of high-quality, full color, and energy efficient displays.
First, shadow and ghost images will be inevitable because along each light propagation direction several light switches could be activated at same time and shadows of upper stream pixels would be cast onto down stream pixels.
Second, optical efficiency is inherently low. In order to achieve an acceptable uniformity or to minimize shadow images light extraction at each light switch has to be very low so that the light flux throughout the waveguide is not significantly attenuated. Consequently, only a small portion of the light inside a waveguide can be utilized.
Third, full-color and gray-scale displays will be difficult. Colors are achieved by using multilayer band-pass filters coated on the waveguide. The complexity and cost of depositing such filters on closely spaced areas is high. Gray scales are achieved by using area weighting and temporal weighting methods. The area weighting control uses a plurality of light switches of varied sizes on each pixel. A gray scale is obtained by turning on a number of light switches that add up to a total area proportional to the gray scale. A large number of light switches must be used on each pixel in order to achieve decent gray scales. Temporal weighting control requires either a line-scan or an active matrix-addressing scheme. A line-scan with gray-scale control demands a switching time of nano-seconds. It is not clear, at this time, whether such a short switching time can be achieved with a relatively large (several hundred micrometers across) electromechanical switch. The use of an active matrix will significantly increase the cost of the display.
Therefore, there exists a need for an inexpensive, simple, energy efficient, high quality, fill color FPD that can be manufactured in sizes ranging from several inches to tens of feet.
Furthermore, none of the aforementioned FPD technologies has a low-cost and high-precision build-in interactive capability. In particular, none of the previously described FPDs can be used as a scanner that would allow one to easily convert printed materials into electronic documents.
This invention relates to a waveguide based optical device that is simple to construct, requires low power consumption, allows the formation of video images of good quality and high resolution, and has interactive capabilities. The present invention relates to an optical relay device comprising:
(a) an optical waveguide having first end constituting a single-terminal optical port and a front side constituting a multiple-terminal optical port;
(b) a predetermined number of light switches in proximity to said optical waveguide, said light switches containing optical means for reflecting light waves;
(c) finite and changeable gaps between said light switches and said waveguide; and
(d) means for changing said gaps thereby actuating said light switches and relaying optical signals between two said ports.
The present invention also relates to an optical display device comprising
(a) an optical waveguide plate including a predetermined number of optical waveguides, said optical waveguides having a first end and a second end capable of receiving light waves;
(b) a predetermined number of light switches in proximity to said optical waveguides, said light switches involving optical means for redirecting light waves;
(c) finite and changeable gaps between said light switches and said optical waveguides;
(d) means for changing said gaps thereby actuating said light switches;
(e) at least one light source consisting of an array of light emitting elements, said light source being coupled with said optical waveguides through at least one end of said optical waveguides, said light emitting elements emitting light waves of controllable intensities; and
(f) control means, including control circuits, for producing images by controlling actuation of said light switches and light emission from said light source.
The present invention also relates to a method for displaying an image comprising:
(a) emitting an array of light waves from an array light source into an optical waveguide plate containing a plurality of optical waveguides, said array light source containing a plurality of elements that emit light waves wherein the light emission from each said element can be controlled;
(b) actuating a light switch such that said light switch is moved into proximity to said optical waveguide thereby extracting said light waves from said optical waveguides into said light switch;
(c) redirecting said light waves for viewing; and
(d) coordinating actuation of said light switches with light emission of said array light source such that a light image is formed.
The present invention solves the problems of low light extraction efficiency, high-energy consumption, image shadow, slow speed, and high manufacturing cost of prior art displays.
The foregoing merely summarizes certain aspects of the present invention and is not intended, nor should be construed, as limiting the invention in any manner. All patents and publications cited herein establish the state of the art and are hereby incorporated by reference in their entirety.